**EVOLUTION TITLE

Principles of Evolutionary Biology

The modern study of animal behavior dates to the work of Charles Darwin (b. 1809 d. 1882)

Darwin published several works that dealt heavily with Animal Behavior:

-On the Origin of Species by Means of Natural Selection (1859)

-Variation of Animals and Plants Under Domestication (1868)

-Descent of Man and Selection in Relation to Sex (1871)

-Expression of Emotions in Man and Animals (1872)

Darwin's Dogma: These are the observations that led Darwin to propose his theory of evolution by natural selection.

**DOGMA TEXT

The dogma is the foundation of modern evolutionary biology, including animal behavior, that was put forth in Darwin's book, The Origin (above). The dogma has three main parts.

Part 1. Adaptation- We can observe that species are apparently tailored to a particular lifestyle. In other words, there is a close match between a species' form (morphology) and its behavior with its particular ecological situation. Evolution by natural selection tries to explain how adaptation comes into existence.

Examples: Arctic mammals have thick fur; marine mammals have blubber

**FUR/BLUBBER

Part 2. Descent with modification- Living beings never arise spontaneously, but are always born to parental animals. Furthermore, offspring tend to resemble their parents. If we follow this observation to its logical conclusion, and allow that offspring are not perfect copies of their parents, we must conclude that new species are always derived from old ones.

**DESCENT TEXT **SAMPLE PHYLOGENY

This is a KEY POINT: It means that any two species of animals can be traced back to a single common ancestor species

Part 3. Natural selection- More offspring are born than survive. Because most individuals do not make it to adulthood, there is a struggle for existence (competition). Some individuals (for whatever reason) possess features that make them more likely to survive and reproduce. If offspring tend to resemble their parents (see part 2), the natural selection can lead to evolution.

**NATURAL SELECTION TEXT

Natural selection does not always lead to evolution (we'll see why later), but it is an important force causing evolutionary change. Evolution by natural selection explains adaptation.

We can consider some examples that illustrate the main parts of Darwin's dogma.

A. Evidence for Adaptation: Similar structures and/or behaviors are used to solve similar problems by different, distantly related species.

**ADAPT. EXAMPLE: LAMPSILIS 1 **ADAPT. EXAMPLE: LAMPSILIS 2 **GLOCHIDIA **Lampsilis MOVIE

B. Evidence for descent with modification: Because all living species are descended from earlier species, evolution is historical. In other words, the present (the behavior of species we see today) is influenced by the past, like human history.

We can learn how animal behavior has changed over time, and how the behavior that evolved came into being, by studying what behavior came before in the evolutionary past.

We can do this in two ways: by using the fossil record, and by comparing behavior among living species.

We can represent the patterns of evolutionary relationships among species by using a special diagram called a phylogenetic tree. Think of the tree as a pedigree or family history- in fact that is exactly what the tree is.

**EXAMPLE PHYLOGENY

Pedigree- puts ancestors at top and shows descendants below.

Phylogenetic tree- puts ancestor species at bottom, present species at top.

How do we get these trees? How can we determine the historical evolutionary relationships between species or groups of species? The simple answer is that, on average, we expect more similar species to be more closely related.

We must look for fundamental similarities within groups of species: those shared characters that define evolutionary relationships (common ancestry).

Example- mammals have fur, produce milk from modified sweat glands, and have 3 bones in the inner ear.

**MAMMAL PHYLOGENY

BUT... important complications arise (often due to adaptations):

**JAY-PENGUIN-SEAL

1. There are differences in morphology and behavior (sometimes dramatic) among closely related species.

2. There can be surprising similarities among unrelated species.

Example- Jay and Penguin are close relatives (both are birds. What fundamental similarities do they share?).

Seals (mammals) and Penguins (birds) share fins, thick body insulation, water-resistant covering, streamlined body. Both are radically different from most other mammals & birds!

To uncover the history of evolution, we must be able to tell shared features (similarities) that result from common ancestry from those caused by natural selection (adaptation).

There are three major evolutionary patterns that you should be familiar with:

**TREE/PATTERNS

 I. Divergence- Species or groups of species with recent common ancestry evolve to have very different features

II. Convergence- Species or groups of species with distant common ancestry evolve to have similar features

III. Adaptive radiation- The descendants of an ancestral species fill a wide array of new lifestyles (ecological roles).

 When radiations occur, some species will converge on non-related animals, and they will evolve to be different from their ancestors and close relatives.

Examples-

**GALAPAGOS MAP **DARWIN'S FINCHES **MARINE IGUANA **HAWAIIAN BIRDS

Homology is the term for similar features that are inherited from common ancestors.

Analogy is the term for similar features that result from natural selection (convergence).

 Homology example- fore limb of mammals

Analogy example- wings of....

**LIMB MORPHOLOGY **WHALE LEGS **HUMMIE/ARCHAEOPT. **LEMUR/SQUIRREL **GECKO/DRAGON **FROGS

C. Evidence for evolution by natural selection: Darwin was inspired with this idea in part by observing and studying the results of controlled breeding of animals and plants.

Farmers and herders have practiced artificial selection for thousands of years by deciding which individuals mated with each other.

One of the most dramatic examples of the effects of artificial selection is domestic dog breeds. Dogs may be the most behaviorally and morphologically diverse species in existence.

**4 DOG BREEDS **2 SHEEPDOGS **SAMURAI CRAB

Again, Darwin noted that in nature, animals' reproductive rates are high, but populations are usually stable or fluctuate (populations rarely grow steadily over time. What species is a dramatic exception to this?). Many more individuals are born than make it to adulthood.

**E coli DIVISION

Example- Bacterium Esceriscia coli divides every 20 min.;  72 generations per day = 2 to the 72nd bacteria in one day. Approx. 5,000,000,000,000,000,000,000 bacteria (5 septillion)  

Malthus- Early 19th century (before Darwin). Proposed that there are natural checks or "brakes" on population growth.

 **DARWIN TEXT

Darwin proposed that evolution proceeds by natural selection: Natural selection leads to changes in species over time.

**CONDITIONS TEXT

-IF individuals vary within species- variation affects ability to survive and reproduce (fitness)

-AND variation is heritable- offspring tend to resemble their parents

-THEN heritable factors that increase fitness will be better represented in future generations

We now know that sequences of DNA molecules (genes) are the heritable factors that cause evolutionary change. Darwin figured this out WITHOUT knowledge of genetics!

**EVOLUTION TEXT

Because all biological evolution follows the rule of descent with modification, evolution is historical. Just as in human history, the present (species that we can actually observe and measure) are influenced by the past (ancestral species that have gone extinct).

This fact leads us to the principle that the structures and behaviors of animals that we observe can give us clues to their evolutionary history.

The Comparative Method- is the most powerful approach we can use to analyze the evolution of behavior. This approach uses the traits of extant (living, as opposed to extinct) species to determine and reconstruct probable evolutionary pathways.

There are two main types of comparative study.

 -We can measure correlational relationships between traits of interest in many different species, and then ask whether evolutionary change in one trait is associated with evolutionary change in the other trait.

Example: Effects of social structure on the evolution of testes size in primates (monkeys and apes).

**TESTES SIZE TEXT

 Hypothesis: Greater sperm numbers, indicated by larger testes size, will be advantageous to males if females copulate with different partners. Males with more sperm are more likely to father the young when they are competing with other males at copulation time; we also assume that there is some evolutionary cost (disadvantage) to having very large testes.

**FEMALE/MALE DIFFERENCES

 Prediction: Primate species with multi-male social groups will have larger testes (relative to the rest of their bodies) than those species with monogamous pairs or single male groups.

-Species that are usually monogamous: Humans, Gibbons **MONOGAMOUS EXAMPLES

-Species that usually have single-male groups: Gorillas **1 MALE EXAMPLE

-Species that usually have multi-male groups: Chimps **MULTIMALE EXAMPLE

 Results of the analysis: Testes size does appear to be greater in multi-male groups.

**PLOT OF DATA  **BAR GRAPH

 The problem with this type of analysis is that, statistically, we are assuming that all of the species evolved INDEPENDENTLY. Why do we know that this is not a valid assumption?

**NON-PHYLOG ASSUMPTION **MORE REALISTIC TREE 

To address this problem, scientists have developed... 

**PC TITLE

Phylogenetic comparisons provide a more valid approach . The main idea is to somehow take the structure of the phylogeny directly into account in the analysis.

-The structure of the evolutionary tree for the species you are studying is first estimated. This is done by measuring the degree of similarity among the species. Remember that we must try to identify homologous similarities among species to do this.

**CHARACTER MATRIX

-The phylogenetic tree can help inform us about how our trait changed over evolutionary time.

-We can also use the information in the evolutionary tree to help us estimate how much similarity among species is caused by common ancestry.

-After we do that, we can factor out the effects of common ancestry (homology)- any similarity among species that remains probably results from adaptation.

How phylogenetic comparisons are done: One set of recently-developed phylogenetic approaches uses the tree of evolutionary relationships to mathematically calculate the relative effects of ancestry and adaptation in the evolution of your trait of interest.

Continuous characters- Independent contrasts. Predator evasion and body armor in lizards.

**INDEP CONT TEXT **SAMPLE PHYLOGENY- TRADEOFF **LIZARD PHYLOGENY/DATA **LIZARD PLOT  

**BEH ECOL TITLE

 The branch of animal behavior that focuses on studying the adaptive value of behavior is called behavioral ecology.

 Another definition of adaptation: A form of a trait that gives individuals an advantage in transmitting genes to next generation over other forms of the trait.

-Note that this definition requires that there is variation for the trait of interest within a population or species.

 Adaptations increase the Reproductive Success (RS) of individuals, relative to other individuals in the population.

-Note: In practice, measuring reproductive success in nature is difficult!

**RS EXAMPLE

Ideally, RS would be measured over lifetime of individuals. This is not practical in most cases.

RS has two main components- survival and fecundity.

Two "shortcuts" are often used to test for the adaptive value of different behaviors:

A. Measure RS during part of individual's life span.

Example- You observe a species with a life span of 3 years for 2 months, and extrapolate reproductive and death rates during those 2 months to the entire life span.

B. Measure traits that may correlate with differences in RS

Examples- Caloric intake; probability of surviving during study period; number of mates observed.

Furthermore, measuring genetic effects on behavioral variation in natural populations is difficult and has rarely been accomplished by biologists (so far, but this ability is increasing rapidly).

 -Therefore, behavioral ecologists often ASSUME that there are genetic effects when they are studying variable behavioral traits and their effects on RS.

An example of a complete study of adaptation: Genetic effects on honey bee behavior and colony performance (R.E. Page and colleagues).

**BEE STUDY TEXT **BEE QUEEN

Main Observation: Honey bee queens mate with many males (as many as 10 to 20 on average), and the number of mates varies among queens.

Hypothesis: the number of matings by honey bee queens is an adaptive trait.

Further observations that help in generating predictions:

1. Multiple mating reduces the levels of genetic relatedness (similarity) within honeybee colonies.

2. Some daughter worker bees have the same father (super sisters), others have different fathers (half sisters). Worker bees within the hive vary in their degrees of genetic relatedness.

3. Worker behavior is known to be influenced by genetic differences. In particular, worker jobs that can influence colony performance, such as the collection of food stores and defensive behavior, have genetic components.

Prediction: Colonies that are more genetically diverse will have higher RS than the less diverse colonies.

The study:

**DESIGN DIAGRAM

-Artificially inseminate queens with sperm collected from 5 different drones. 5 sets of 3 queens each are inseminated with the sperm from one of the males; one set of 3 queens are inseminated with the sperm from all 5 males.

-Allow each queen to raise a colony for one summer.

-At the end of the summer, collect colonies and estimate their RS by measuring colony size, amount of food stored, and amount of reproductive brood (offspring queens and males) produced.

The results: **GRAPH 1 **GRAPH 2

-Multiple-mated queen colonies did not outperform single-mated queen colonies. However, multiple-mated queen colonies were more average on all measures of colony RS.

Conclusion: -Was the original hypothesis supported?

Final note: Behavioral ecology has focused attention on the importance of behavioral diversity and alternatives within species and populations.

**SUNFISH STRATEGIES